Single Eye vs Both Eyes
One eye bulging is usually injury — the betta hit something, scraped a fin against decor, or fought through tank glass with its reflection. Treat with clean water and epsom salt (1 tablespoon per 5 gallons) and the swelling typically reduces in 7-10 days.
Both eyes bulging is almost always bacterial infection or internal disease (kidney failure, dropsy precursor). This is far more serious. Start broad-spectrum antibiotics like Furan-2 or Kanaplex immediately.
Treatment Protocol
Daily 25% water changes with dechlorinated water at 79°F. Epsom salt draws fluid from the tissue and reduces swelling — dissolve fully in a separate cup before adding to the tank.
For bilateral popeye, dose Kanaplex per package directions for 7 days. Feed garlic-soaked food (commercial garlic guard or fresh garlic juice on pellets) to boost immune response.
- ✦Do not use aquarium salt and epsom salt at the same time.
- ✦Remove sharp decor that could re-injure the eye.
Prognosis
Injury-cause popeye has 90%+ recovery with full vision restored. Bacterial popeye drops to about 50% — and even survivors often lose the affected eye. Bettas adapt well to monocular vision and continue to live normally.